Predefined maintenance windows
By default, there are seven predefined maintance windows, one for each day of the week.
The duration of SATURDAY_WINDOW and SUNDAY_WINDOW is longer than that of the other windows.
The predefined maintainance windows can be adjusted with dbms_scheduler.set_attribute.
By default, all predefined maintenance windows use the resource plan DEFAULT_MAINTENANCE_PLAN, but any resource plan can be assigned to any maintanance window by including the subplan ORA$AUTOTASK in the new plan.
Automated maintenance tasks run under its subplan ORA$AUTOTASK. This subplan divides its portion of total resource allocation equally among the maintenance tasks.